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Waste Heat to Electricity – Organic Rankine Cycle

A simple way to conserve energy in buildings is to reclaim heat by converting waste heat to electricity.  In industry, where there is a high temperature process, you could draw heat from the end of a process and put it back into the beginning of the process.  But what if it isn’t practical or possible to do this?

Is it possible to take that waste heat and convert it to electricity?  The short answer is “Yes”.  Large power plants (fossil fuel and nuclear) have been doing this for years.  They use heat from burning coal or natural gas, or heat from a nuclear reaction to create steam.  The steam turns a turbine to generate electricity.

But what about smaller scale applications?  New technologies have been developed that will take lower temperature waste heat to produce electricity.

One emerging technology is called Organic Rankine Cycle (ORC).  ORC will take temperatures as low as 80C and convert it to electricity.

Organic Rankine Cycle Installed

For example, we recently installed a 125 kW ORC system onto a high-temperature exhaust stream.  The ORC system produces 890,000 kWh per year with a 27% annual return on investment and a 4 year project payback.  The amount of electricity is limited by the local utility company.  They do not allow any electricity from the ORC system to feed back to the grid; it all must be used in the building.  Once these rules are relaxed, the ORC system will be capable of producing an additional 200,000 kWh, and sell it to the grid.